Worksites, such as, for example, mine sites, landfills, quarries, construction sites, etc., commonly undergo geographic alteration by machines and/or workers performing various tasks thereon. It is thus useful to generate a three-dimensional (3D) terrain map of these work sites.
Photogrammetry is a technique for generating 3D terrain maps. Generally, photogrammetry generates a 3D terrain map of an area being surveyed by combining a plurality of overlapping aerial images of the area. However, sometimes the 3D terrain map generated by photogrammetry has some errors, which renders the map not accurate enough for some applications. To improve the accuracy of the 3D terrain map, ground control points (GCPs) are used for calibrating the 3D terrain map. The GCPs are landmarks with known accurate global locations, i.e., latitude, longitude, and elevation. They are placed manually at different locations in the area being surveyed. These GCPs are also visible in the 3D terrain map generated by photogrammetry. The difference between the accurate global locations of the GCPs and their estimated locations in the 3D terrain map generated by photogrammetry is used to compensate for errors in the 3D terrain map.
U.S. Pat. No. 5,596,494 (the '494 patent) discloses a method of generating maps using photogrammetry. The method includes navigating flight and acquiring images of terrestrial scenes, setting up and collecting geophysical coordinates of GCPs under flight paths, and processing the acquired images to derive absolute geophysical coordinate information using camera parameters and geophysical coordinates of the GCPs.
However, the method disclosed in the '494 patent requires manually setting up and collecting the geophysical coordinates of the GCPs in an area being surveyed. Because the area being surveyed usually undergoes geographic alterations, the GCPs may be changed or even disappear due to the geographic alterations. Therefore, new GCPs may need to be set up and their geophysical coordinates need to be collected frequently. The process of setting up GCPs and collecting the geophysical coordinates of the GCPs is time-consuming and expensive, or even dangerous, as it requires travel to the area being surveyed with appropriate equipment and personnel.
The disclosed methods and systems are directed to solve one or more of the problems set forth above and/or other problems of the prior art.